Method of preparing high molecular weight organosiloxane polymers



wax. v.- 63

Patented June 1, 1965 This invention relates to a novel method forpreparing high molecular weight organosiloxane copolymers havingtlillerent types of units in each molecule.

it is known that. silicone rubber exhibiting satisfactory physicalproperties can he produced from high molecular weight. essentiallylinear, diorganoslloxane' polymers. Generally these polymers havemolecular weights in the range of l00,000 to 2,000,000 and contain aminimum number ol branehings. it a significant number of trifunctionalpolymeric units (eg. RSiO' units) are present in the polymers. theresulting cured product will generally prove to be brittle. hard and tooresinous in nature for use as an clastomer. Thus. high polymeric,essentially di organosiloxane polymers having an organic substitu ent/silicon ratio in the range of 1.98/1 to 2.02/1 must be used for siliconerubber stocks.

The high molecular weight organosiloxane polymers employed as startingmaterials for silicone rubbers are prepared by relatively simpleprocedures employing various condensation agents when uniform startingmaterials are employed. A low molecular weight dimethylsiloxane polymer,eg. l(CH SiO] can be condensed to a high molecular weight linearsiloxane polymer employing strong acids, alkalies. certain salts.phosphorous-nitrogen compounds and other nitrogen compounds ascatalysts. The polymers produced by these known methods can generally beclassified as homopolymers.

To attain specific properties in silicone rubber, it is often necessaryto prepare high molecular weight diorganosiloxane polymers wherein avariety of units having dilTercnt organic substituents are present. Suchpolymers are classified as copolymers. These copolymers must exhibithigh molecular weight and must be essentially linear (i.e. tree ofbranching in thc chains). It has been proposed to cohydrolyzc mixturesof the corresponding organosiloxanes to produce low molecular weightorganosiloxnne copolymers and thereafter'to prepare the high molecularweight copolymers by known methods from the low molecular copolymers. Oninvestigating this method. however. it was found that some organicgroups are Split oil" by the action of the acids. alkalics or other,

condensation agents employed as additives or produced during thereaction. Even when the cleavage of organic groups is reduced to a minorpercentage, the eopolymers so produced cannot be employed in thepreparation of silicone rubbers. The known methods of polymerization,though useful in the preparation of homopolymers, produce eitherrelatively low molecular weight oils of a few thousand cs. viscosity, at25 C. or resinous materials when applied to the production ofcopolymeric organosiloxnncs.

Another proposed method for preparing high polymeric weightorganosiloxanc copolymer's consists of equilibrating mixtures of lowmolecular weight polysiloxanes (particularly cyclic diorgnnosiloxancs).It has been found, however, that organopolysiloxanes having differentorganic substituents are not miscible with each other in many cases.Vigorous equilibration of a mixture of immiscible orgz'tnosiloxanepolymers in accordance with known procedures results in cleaving organicradicals from some of the silicon atoms, thus producing a copolymerieproduct unsuited for use in preparing silicone rubber. On the otherhand, a slow. cautious equilibration under mild conditions may avoidcleavage of organic substituents but the result of such an equilibrationis separate condensation of the individual siloxane componentsemulsified in each other and no copolymerization occurs.

Another method suggested for preparing the desired org'anosiloxanecopolymers consists of equili'brating mixtures of low molecular weightsiloxancs in organic solvents. This method has proved to beunsatisfactory because the solvents are very diflicult to remove fromthe high molecular' weight siloxane copolymers. Generally the solventequilibration is carried forward employing alkaline condensation agents.The alkaline catalysts are also very ditficult to'rentove front the highpolymer. The traces of alkaline catalyst remaining in the high polymerlead to'signlficnnl deterioration of the thermal and elecchainterminating units in the copolymeric reaction mass.

trical properties of any silicone rubber prepared the-refrom unlesslaborious and costly steps are taken to remove the last traces of suchcatalyst from the high polymer. The removal of the solvents and alkalinecatalyst from the high polymer is costly in time and money and issufficiently difiicult and uncertain to be a production problem for theentire industry.

It is the object of this invention to introduce a novel method forpreparing organosiloxane copolymers of high molecular weight. Thepreparation of copolymeric organosiloxane gums-for use in siliconerubber stocks is also an object of this invention. Other objects andadvantages of this invention are detailed in or will be apparent fromthe disclosure and claims following.

This invention consists of a method of preparing high molecular weightorganosiloxane copolymers by equilibrating the individual, immisciblesiloxane starting materials in stages, employing a phosphorous-nitrogencompound as the catalytic tagent and adding in stepwise fashion thesiloxanc exhibiting the faster condensation rate to the siloxaneexhibiting the slower condensation rate, thus effecting a stepwiseequilibration to produce eopolymers of any predetermined and desiredcomposition.

It is known that different organosiloxanes exhibit differcnt rates ofcondensation. The stepwise addition of the siloxane having the fasterrate of condensation to the siloxane having the slower rate ofcondensation and the parallel stepwise equilibration makes it possibleto avoid the formation of high molecluar weight homopolymers of therapidly condensing siloxane before auniform distribution of theindividual units has taken place. At the same time, it is possible tolimit the chain length and adjust the average moleeular weight of thefinal copolymerie product by introducing triorganosilyl units which actas The triorganosilyt units also prevent the condensation fromproceeding too far in the early stages of the stepwise equilibration andthus insure that the equilibration reaction is not overtaken andreplaced by the condensation reaction.

It was further discovered'that the stepwise equilibration method ofthisinvention not only permits the preparation of copolymers heretoforedittcultly prepared but it also greatly reduces the time required forequilibrating and condensing CllOt'gtlnOSllOXtlflCS. Thus this process isimpler and more economical than the heretofore known equilibrationmethods. Thus the yield of useable high polymer obtainable from theequipment employed can be significantly improved employing this method.

The low molecular weight organosilo'sanes employed in starting materialsherein are polymers wherein at least 98 mol percent of the units are ofthe formula R SiO and up to 2 mol percent of the units are of theformulae RSiO I and R SiO These starting materials have viseo'sities upto 10,000 es. at 25" C. The organic substitu- 3 ents bonded to siliconby C i bonding and represented by R can be alkyl, halogenoalkyl,alkenyl, aryl, aralkyl. alkaryl and haloaryl radicals Such as methyl,ethyl, pro? pyl, butyl, cyelohexyl, cyclobutyl, nonyl, octadecyl, chloromethyl, 3,3,3-trifiuoropropyl, vinyl, ally], I octadecenyl,

phenyl.- biphenyl, phenylethyl, methylphenyl, chlorophenyl, bromoxcnyland fiuorophenyl radicals. Particularly significant as organicsubstituentsherein are the methyl, ethyl, phenyl and vinyl radicals asfound in such siloxane polymers as dimethylsiloxanes, diethylsiloxanes.phenylmethylsiloxanes, phenylethylsiloxanes, phenylvinylsiloXanes andmethylvinylsiloxanes.

The condensation catalysts employed herein are phosphorous-nitrogencompounds selected from phosphoronitrile-halides and certain organonitrogen derivatives of phosphorous acid and phosphoric acid. The phoshoronitrile halides employed are preferably the polymeric chloridesrepresented by the formula (PNCl where 11 is an integer of at least 3.Preferred are those compounds wherein n is 3. 4, 5 or 6 and thecommercially available phosphoronitrile chlorides are usually mixturesof such species.

The orgnno nitrogen derivatives of phosphorous or 1 herein arerepresented by the phosphoric acid employed selected from alkyl, aryl,alkaryl-and aralkyl radicals and hydrogen atoms, at least one of'thesubstituentsR and R" being one of the defined organic radicals. R" is analkyl, aryl, alkaryl or aralkyl radical, and X is a halogen atom,preferably chlorine or bromine.

The following compounds are representative of the preferred organicphosphorousmitrogen compounds:

Phosphorous acid-dichloride aniltde C H -NHRCl Phosphorousaciddichloride-methyl-antlide' C H .N CH )--PCl Phosphorousacid-dtchlortde-ethyi-untltde C H -N (C H )PCl Phosphorousuetd-dtehlortde-dtphenylnmtde Phosphorous acid-dtchtortde-methylamlde CHNHPCl i Phosphorous acid-dtchlortde-isopropylamlde (cH cH NH-Pci,Phosphorous acid-dtchlorlde-benzylamtde C H CH -NH PCl, Phosphorousaetd-antit'desantle [C H -N=P-NH-C H 3 Phosphorousaetd-methylamlde-antle C H N=.P-NHCH Phosphoric aetd-dlchlortde-untlideC H NHPCi3 Phosphoric aeld-dtehlortdeamaphthylamtde C1 H7NH'POC1gPhosphoric netd-dichtortde-methylumtde CH NHPOCI Phosphoricaetd-dtehlortdetsopropylamide (CH CHNH?OCt Phosphoricnetd-dtehlortde-ethytamlde C H NHPOCl Pho phoric acidducthylamide-anile.ll Nll-l'a NFsll; ll

Phosphoric aeltl-tsopropylauiide-anile (Ull:l:(llNl[--=:N(Jrll in therange of 40-l2tl" C. and the most preferred re action temperatures arein the range 7090 C. The

- pressures at which reaction can be carried forward vary fromsubatntospheric to snperatmosphcric and atmospheric pressure ispreferred. The reaction pressure is not critical.

In the preferred embodiment, the siloxane (A) having the slower rate ofcondensation is charged to the reaction vessel with the catalyst andsolvent to be employed. The siloxane (B) having the more rapid rate ofcondensation is added stepwise to the reaction vessel with the'initialportion of siloxane (B) being from 0.25

. to 2.0 times the quantity of siloxane (A) charged tothe fected a whiteturbidity.

vessel. The initial quantity of siloxane (B) added will depend upon thedifference between the reaction rates of the equilibration and thecondensation reactions. The

faster siloxane (B) condenses to form high polymers in comparison tosiloxane (A), the smaller the proportion ofsiloxane (B) employed in eachstep must be. In general, the initial addition of siloxane (B) should beabout 0.5 times the initial charge of siloxane (A) in the reactionvessel. After each addition of siloxane (B) the reaction mixture isstirred and heated until a clear, homogeneous reaction mass is obtainedevidencing a complete equilibration has occurred. This stepwiseprocedure has a reaction time which is the sum of all the individualsteps and is much less than the time required for the reaction when theentire mass of siloxane (B) is added at one time to siloxane (A) and theequilibration and condeusation is carried forward to completion. Ofcourse, it is frequently found that the equilibration will not occur atall when the two siloxanes are admixed in a single step reaction.

The following examples are included herein to aid those skilled in theart to obtain a clear understanding of this invention. The scope of theinvention is delineated in the claims and is not limited by theexamples. All parts and percentages in the examples are based on weight,

all viscosities are measured at 25 C. and all temperaturesare in degreescentigrade unless otherwise stated.

EXAh'iPLE l A mixture of 20 g. of phenylmethylpolysiloxane (A) with aviscosity of 1050 cs.. 5 g. dimethylpolysiloxane .(B) with 11 viscosityof 2,000 es. and 0.3 g. of a trimethylsilyl cndblocked dimethylsiloxanewith 12 silicon units (Si-l2) was mixed with 0.1 ml. of a 50 percentsolution of (PNCl in methylene chloride at a temperature of 85 whilestirring thoroughly. After the original white-turbid mixture had clearedanother 5 g. of the same dimcthylpolysilortane were added. which againef- Other additions of dimethylpolysiloxane followed after the previousmixture had cieared. Table I gives the time in which the equilibrationrttns off, detailed after the individual additions. The velocity of thereaction and the ratio of phenylzmethyi groups follow from therefractory indices. The end product was a highly viscous transparentpolymer which was suitable for preparing silicone rubber.

Table I (.fomposition of NHL mixturev Refractive than of v m n uEquilihrn- Index of sllosumtion tlnw the mixlt, Lotti] HiloxnneSiloxzutt in minutes l11|"( ('t1lllcs. A, Loot) It, 2.000 .posltioti cs.vs.

. ill ..r LBW: 5 .311 5 4'! 1.51443 (1 .311 ll) .51) 1 1000 "r 2t] 15JO 1. tstts 5 2t) 21] 111 l. 47 ill 2U 3U Ill 1. 4095 1t) 2t) 4t) 5 l.4523 1t) 2. 5t] ,5 1.4413 1t) Bl) (it) 3 1. 4383 30 20 90 5 1.4318 .3020 120 5 1.4258

Equitihrtitlun time in minutes: 2 hours-H8 minutes.

EXAMPLE 2 i A mixture of the'same components of Example 1 of 20 g.phenylmethylpolysiloxane (A), 10 g. of dimethytpolysiloxane (B) and 0.3g. Si-12" was equilibrated and condensed asin Example 1. Table II givesthe quantities of dimethylpolysiloxane added stepwise and the corresponding equilibration time. As in Example 1 the end product was ahighly viscous polymer, suitable for preparing silicone rubber.

3 hrs.+45 minutes EXAMPLE 3 A mixture of the same components as inExample 1 of 20 g. phenylmethylpolysiloxane (A), 40 g.dimethylpolysiloxanc (B) and 0.3 g. Si-12f was equilibrated andcondensed stepwise as in Example 1. Table III gives the quantitiesofdimethylpolysiloxane added stepwise and the correspondingequilibrationtimes. The end product is like that of Example 1.

Table III i Composition of mixture Addition of Equilibrntion silmtune B,time I in 2,000 es. Siloxnne A, Siloxane B, minutes 1, U50 cs. 2, 000cs.

mixture of the same componentsof Example .1;"

6 20 g. pllCn)i!1lCli1)'iDUi}SiiOXttllC, lit) g. dimcthylpolysiloxoneand 0.3 g. Sil2 is mixed with 0.1 ml. of a 50 percent solution of (lNCl'l in methylene chloride at a temperature of 80 -85" and kept therewhile stirring constantly. 'lhc milky mixture will first clear after 28hours. The end product is like that of Example 1.

EXAMPLE 5 A mixture of 20 g. phenylmcthylpolysiloxnne (A) with itviscosity of 5.0110 cs. 5 g of dimethylpolysiloxane (B) with a viscosityof H1000 es. and 0.1 g. of a sym.-diphenyldivinyldimethyldisiIoxnne(.Sidij) is equilibrtttcd and condensed stepwise under the omeconditions as Example I. Table IV gives the quantities ofdimcthylpolysiloxane added stepwise and the corresponding equilibrationtimes. The end product is a high viscosity, transpurcntpolymer suitablefor the preparation of silicone rubber.

Table IV i toniposition ol mixture Addition of F Eqti lihrntion siloxunu1i, i ti 'tt 1 in 1U,()t1ll(' Filuxnflt A. Sttoxmteti, m.uutes 5, 1h)('5. to. out) cs. G, G, i U. trr i ".i 5 .U I ll) 51] 5 l on as 5 l 2o111 I 2') so 15 Hi It) 4" 11) 10 .U 10 10 2o no 5 an I 2n on 5 3U L'tlI20 5' I 4 hours.

EXAM PLE 6 A mixture of the components of Example 5 of 20 g.phenylmethylpolysiloxttne. 120 g. dimcthylpolysiloxane and 0.1 Si- 11"is mixed with 0.1 g. of the previously used (PNCI M solution at 80"-85and kept there while stirring constantly. The turbid mixture had notcleared after 64 hours ot reaction time.

EXAMPLE 7 A mixture of 20 g. vinylmethylpolysiloxane (C) with aviscosity of 6.000 cs., 10 g. of dimethylpolysiloxane (B) with aviscosity of H000 cs. and 0.1 g. Si-l2 is mixed with 0.1 ml. of the(PNCl solution at a tem peruture of 45-50 while stirring well. Theturbid mixture will clear after 20 minutes. Further quantities ofdimethylpolysiloxane added and the corresponding equilibration times maybe taken from Table V. The end product is a high viscosity transparentpolymer, suitable for preparing silicone rubber.

40 minutes.

EXAMPLE 8 A mixture of 20 g. pheiiyl ethylpolysiloxane o with aviscosity of 500 cs. 5 g. of dimethylpolysiloxane (B) with a viscosityof L050 cs. and 043 g. Si-l2" is mixed with (1i g. of the ordinary tPNClsolution at 35" white stirring well. The milky-turbid mixture clears i ll 7 alter 40 minutes. Further quantities of the samedimcthylpolysiloxane added stepwise and the Corresponding equilibrationtimes may be taken from Table VI. The equilibratcd and condensed endproduct is a transparent, highly viscous polymer, suitable for preparingsilicone rubber.

3 hrs. and 5 min,

EXAMPLE 9 A mixture of the components of Example 8 of 20 g.phenylethylpolysiloxane. 120 g. dimethylpolysiloxane and 0.3 g. Si-l2"is mixed with 0.1 g. of the common (PNCl tg, solution at a temperatureof 8085 and stirred constantly. The milky-turbid mixture will clear onlyaltei 50 hours. Th end product is like that of Example 8.

That which is claimed is:

1. A method of preparing high molecular weight essentially lineardiorganosiloxane copolymers suitable for the production of siliconerubber having an organic substituent/silicon ratio of from 1.98/1 to2.02/1, on the average. and wherein the organic substitucnts bonded tosiiicon through Si-C linkages are selected from the group consisting ofalltyl, halogenoalkyl, alkenyl, aralkyl, aryl, halogenoaryl. and alkarylradicals consisting essentially of equillbrating at least twoimmiscible, low molecular weight, fluid diorganosiloxane polymersemploying stepwise addition of (B) the low molecular weight siloxanepolymer having the more rapid rate of condensation, having a viscosityup to 10,000 cs. at 25 C., containing at least 98 mol percent ofdiorganosiloxane units, any remaining units being selected from thegroup consisting of morioorganosiloxane units and triorganosiloxaneunits where each organic substituent is selected from the groupconsisting of alltyl, halogenoalkyl, alkenyl, aralkyl, aryl,halogenoaryl and alkaryl radicals, to (A),the low molecuiar weightsiloxane polymer having the slower rate of condensation, having aviscosity up to 10,000 cs. at 25 (1., containing at least 98 mol percentof diorganosiloxane units, any remaining units being selected from thegroup consisting'of monoorganosiloxane units and triorganosiloxane unitswhere each organic substitucnt is selected from the group consisting ofalkyl, halogenoalkyl, alkenyl, aralkyl, aryl, halogenoaryl and alkarylradicals, said siloxane (B) being added in successive steps inproportions of front 0.25 to 2.0 times the quantity of siloxane (A)present, the resulting mixturcbeing equilibrated to form a homogeneousmass prior to further additions of siloxane (B), said equilibrationbeing carried forward in the presence of .001 to 1 percent by weightbased on the weight of siloxane polymer present of a phosphorousnitrogen compound selected from the group consisting of ii is an integerof at least 3, R and R are selected trout the group consisting ot :uyl,alkyl. alkaryl and aialltyl radicals and hydrogen. at least l ot thesubstitucntsR and R being one ot' the delincd organic radicals, it" is asubstiluent selected from the group consisting of all'tyl, aryl, aralkyland alkaryl radicals and X is a halogen atom. I

2. The method of claim 1 wherein the siloxane polymer (lit is adimcthylsiloxauc polymer.

3. The method of claim 1 wherein the siloxanc polymer (A) is selectedfrom the group consisting of phenylmt'thylsiloxancs,vinylmcthylsiloxancs and phcnylethylsiloxanes.

4. The method of claim 1 wherein the equilibration is carried forward ata temperature in the range from room temperature to 120 C.

5. The method of claim 1 wherein the catalyst employed is aphosphoronitrile halide.

5. A method of preparing essentially linear, diorganosiloxane polymersof at least 100,000 cs. viscosity at 25 C, suitable for production ofsilicone rubber, having an average organic subsituent/silicon ratio inthe range from 1.98/10 to 2.02/10. wherein the organic substituents arebonded to silicon through CSi bonding and are selected front alklyradicals. halogenoalkyl radicals, aryl radicals, halogenoaryl radicals,alkenyl radicals, aralkyl radicals and alkaryl radicals, comprisingcontacting (A) at least one fluid, low molecular weight diorgaaosiloxanepolymer having a viscosity up to 10,000

cs. at 25 C., containing at least 98 mol percent of di-- organosiloxaneunits. any remaining 'units being selected from the group consisting ofmonoorganosiloxane units and triorganosiloxane units where eachorganicsubstituent is selected front the group consisting of alkyl,halogenoalkyl, alkenyl, aralkyl, aryl, halogenoaryl and alkarylradicals, with (B) a fluid, low molecular weight diorganosiloxancpolymer immiscible with (A) and having more rapid condensation rate than(A) and having a viscosity up to 10,000 cs. at 25 C.. containing atleast 98 mol percent of diorganosiloxane units, any remaining unitsbeing selected from the group consisting of monoo'rganosiloxane unitsand triorganosiloxane units where each organic substituent is selectedfrom the group consisting of alkyl, halogenoalkyl, alkenyl, aralkyl,aryl, halogenoaryl and alkaryl radicals, in the presence of .001 to 1percent by weight based on the weight of siloxane polymers presentomen),

wherein n is at least 3, R and R are selected from alkyl, aryl, alkaryland aralkyl radicals and hydrogen, at least one of the substituents Rand R being oneof the defined organic radicals, R" is selected fromalkyl, aryl, aralkyl and alkaryl radicals and X is a halogen atom, saidpolymer (8) being added in stepwise fashion to said polymer (A), each ofthe stepwise additions of (B) being in an amount of from 0.25 to 2.0times the quantity of the siloxane present, the resulting mixture beingcquilibrated to a homogeneous mass prior to further additions ofsiloxane (B).

I. The method of claim 6 wherein the siloxane polymer (B) is adimethylsiloxane polymer.

8. The method of claim 7 wherein the siloxanc polymer (A) is selectedfrom the group consisting of phenylmethylsiloxane, vinylmethylsiloxaneand pheny1ethylsiloxanc.

References Cited by the Examiner UNITED STATES PATENTS 2,830.967 4/58Nitzsche et al. 260--46.5

MURRAY TILLMAN, Primary E.\'(Tllllltll'.

LOUISE l. QUAST, Examiner.

UNIT D STATES PATENT OFFIKCE-I CERTIFICATE e1 CGRREQTION Patent NO.3,186,967 June '1 1965 Siegfried Nitzsche et a1.

It is hereby certified thet error appears in the above numbered pat.-

ent requiring correction and that the said Letters Patent should read ascorrected below.

' Column 6, Table IV, for the heading Siloxane A, 5, 00 C5 read SiloxaneA, 5,000 cs. under the same heading, under "G. 'the dash should read 2OA Signed a d sealed thi'e ll' th day of January 1966.

(SEAL) Attest: v

ERNEST W. SWIDER r I EDWARD J-. BRENNER Att esting Officer I I l 6.Commissioner of Petents

1. A METHOD OF PREPARING HIGH MOLECULAR WEIGHT ESSENTIALLY LINEARDIORGANOSILOXANE COPOLYMERS SUITABLE FOR THE PRODUCTION OF SILICONERUBBER HAVING AN ORGANIC SUBSTITUENT/SILICON RATIO OF FROM 1.98/1 TO2.02/1, ON THE AVERAGE, AND WHEREIN THE ORGANIC SUBSTITUENTS BONDED TOSILICON THROUGH SI-C LINKAGES ARE SELECTED FROM THE GROUP CONSISTING OFALKYL, HALOGENOALKYL, ALKENYL, ARALKYL, ARYL, HALOGENOARYL, AND ALKARYLRADICALS CONSISTING ESSENTIALLY OF EQUILIBRATING AT LEAST TWOIMMISCIBLE, LOW MOLECULAR WEIGHT, FLUID DIORGANOSILOXANE POLYMERSEMPLOYING STEPWISE ADDITION OF (B) THE LOW MOLECULAR WEIGHT SILOXANEPOLYMER HAVING THE MORE RAPID RATE OF CONDENSATION, HAVING A VISCOSITYUP TO 10,000 CS. AT 25*C., CONTAINING AT LEAST 98 MOL PERCENT OFDIORGANOSILOXANE UNITS, ANY REMAINING UNITS BEING SELECTED FROM THEGROUP CONSISTING OF MONOORGANOSILOXANE UNITS AND TRIORGANOSILOXANE UNITSWHERE EACH ORGANIC SUBSTITUENT IS SELECTED FROM THE GROUP CONSISTING OFALKYL, HALOGENOALKYL, ALKENYL, ARALKYL, ARYL, HALOGENOARYL AND ALKARYLRADICALS, TO (A) THE LOW MOLECULAR WEIGHT SILOXANE POLYMER HAVING THESLOWER RATE OF CONDENSATION, HAVING A VISCOSITY UP TO 10,000 CS. AT25*C., CONTAINING AT LEAST 98 MOL PERCENT OF DIOGANOSILOXANE UNITS, ANYREMAINING UNITS BEING SELECTED FROM THE GROUP CONSISTING OFMONOORGANOSILOXANE UNITS AND TRIORGANOSILOXANE UNITS WHERE EACH ORGANICSUBSTITUENT IS SELECTED FROM THE GROUP CONSISTING OF ALKYL,HALOGENOALKYL, ALKENYL, ARALKYL, ARYL, HALOGENOARYL AND ALKARYLRADICALS, SAID SILOXANE (B) BEING ADDED IN SUCCESSIVE STEPS INPROPORTIONS OF FROM 0.25 TO 2.0 TIMES THE QUANTITY OF SILOXANE (A)PRESENT, THE RESULTING MIXTURE BEING EQUILIBRATED TO FORM A HOMOGENEOUSMASS PRIOR TO FURTHER ADDITIONS OF SILOXANE (B), SAID EQUILIBRATIONBEING CARRIED FORWARD IN THE PRESENCE OF .001 TO 1 PERCENT BY WEIGHTBASED ON THE WEIGHT OF SILOXANE POLYMER PRESENT OF A PHOSPHOROUSNITROGENCOMPOUND SELECTED FROM THE GROUP CONSISTING OF